Sound creating device



y 1939- w. A. GARRATT 2,158,537

SOUND CREATING DEVICE Filed June 25, 1937 Q Patented May 16, 1939 UNITED STATES PATENT OFFICE SOUND CREATING DEVICE Application June 23, 1937, Serial No. 149,928

11 Claims.

This invention relates to horns and is particularly directed to a horn in which the sound is created by the application of air under pressure. Air horns, as heretofore designed, have incorporated valves. The present invention results from the discovery that a valve is unnecessary. The concept, therefore, consists of an air horn structure which is valveless and which incorporates an arrangement of chambers and passageways creating a relative large volume of sound through the application of very little air pressure. This sound is not harsh or raucous but, on the contrary, is melodious.

It has been one of the objects of this invention to provide a horn of this character which produces the necessary warning signal for a vehicle and which will attract attention within the correct range without irritation to those in front of the car. The structure is designed to produce a sound which demands attention, but which does not frighten.

It is the intention herein to claim all uses of the structure disclosed, or its equivalents. That is to say, the vibratory force set in motion by the application of the air to the device may be utilized not only for sound purposes of all sorts but may be used, for instance, for the purpose of velocity increase as in a supercharger.

Briefly stated, the objects of this invention have been achieved in a device which utilizes the reaction of a resonator to produce periodic fluctuations in the discharge rate of a jet of air. This reaction operates either directly or is further directed and controlled through the provision of a jacket surrounding the opening into the resonator, or

through the intervention of a perforated dia-' phragm to amplify the effect.

Also, resonant conditions in other parts of the device may be utilized to increase and to change the quality of the sound produced.

Any sort of air pressure producing device may be utilized, such as an electrically operated piston or, in its simplest form, the ordinary hand pressed bulb. likewise, any type of sound directing medium may be used when desired, such as a long, straight flared tube, a circularly arranged flared tube, or a reflector.

Other objects and certain advantages will be more fully apparent from a description of the accompanying drawing in which:

Figure 1 is a general view of the horn.

Figure 2 is an enlarged fragmentary view of the sound creating unit.

Figure 3 is an exploded View showing the sepa rate parts of the unit.

Figure 4 is a sectional View taken on line 4-4, Figure 2.

Figure 5 is a sectional view taken on line 5-5, Figure 2, detailing the escapement openings for permitting full pulsations or entirely suppressing undesirable sound waves.

Figure 6 is a sectional view taken on line 5-6, Figure 4, illustrating the passageway and chamber arrangement of the fully refined form of the invention.

Figure 7 is a detailed sectional view of the jet orifice showing the counterboring thereof.

The device, reduced to its simplest component parts, consists of a cavity It] with an orifice l l into which is directed a jet of air.

The cavity with the orifice forms a resonator. When air is directed into the opening, through a tube l2 having a similar orifice l3, pressure is built up in the cavity and eventually reaches a value which will drive the air out again even against the jet. An excess of air will pass out, due to the momentum of the air in and near the orifice, causing the pressure in the cavity to fall below normal. Air from the jet will now enter again, and the cycle will be repeated. The frequency of such a cycle depends primarily on the size and character of the orifice and the volume of the enclosure. The larger the volume, the longer the time which will be required for the building up and reduction of pressure through a given sized orifice and, hence, the larger the volume, the lower the pitch. The larger the orifice the more quickly the pressure variations can take place, and, hence, the larger the orifice, the higher the pitch.

The frequency of response of such a device generally corresponds to a wave-length of compressional waves in air much greater than the dimensions' of the cavity. Internal reflections from the walls of the cavity have, therefore, very little influence on the action which takes place, the

pressure being sensibly the same throughout the cavity, at any instant. Hence, standing waves of any importance are not likely to develop and the resonator will respond principally to but one frequency and very little, if at all, to harmonics or overtones.

Due to the action just described, the impinging jet is alternately admitted to the orifice during ingress of air to the cavity, and blown aside during the period of egress of air from the orifice. This causes alternate rarefaction (due to entrainment of air with the jet) and compression of the air in the neighborhood of the orifice, and, if the frequency of the cycle is within the audible range, a sound will be produced.

The maintenance of oscillations in this device depends on the instability, turbulence, and friction accompanying the motion of air streams. If there were no friction or turbulence, air could flow in through the central portion of the orifice and out around the periphery without causing any periodic pulsations. Factors tending to increase turbulence in the neighborhood of the orifice will, therefore, aid in the functioning of the device.

During the part of the cycle when the air is escaping from the resonator, the orifice acts as a reverse jet causing a variation of pressure to travel back along the stream of oncoming air in the driving jet. If the tube l4, connected to the jet-tube I2, is of appropriate length, a resonant condition may be set up which will add to the disturbance of the jet already described and increase the volume of sound produced. Any type of device may be connected to the tube 14 for supplying the air stream. A hand pressed bulb I5 is shown in this instance.

If now the opening around the jet be jacketed, by means of a casing Hi, there will be produced in the jacket periodic variations of pressure as the air-stream alternately discharges into the resonator cavity or is forced to blow radially into the jacket. The frequency of these alternations will be controlled, primarily, by the natural frequency of the resonator modified slightly by the jet-tube resonance and by the impedance to air flow introduced by the jet disc and jacket. It is to be noted that the resonating cavity acts as a sort of escapement which times the flow of energy from the air stream much as the balance wheel of a watch, by being set into oscillation, times the pulses of energy which are discharged from the mainspring.

The acoustic power output of this device may be further increased by attaching a properly designed horn I! to the opening of the jacket. The horn serves also the purpose of directing the sound emitted.

In the device, as above described, the reaction of the resonator on the jet is due entirely to the disturbance of the jet by air being expelled from the resonator orifice. A more effective control of the jet may be obtained by the provision of a perforated diaphragm l8 which is placed between the jet-tube orifice l3 and the resonator orifice II. The diaphragm includes the central opening IS in line with the jet and resonator orifice and larger than these openings so as not to break up the jet originally. If the natural frequency of vibration of such a diaphragm is considerably higher than that of the resonator, the diaphragm will vibrate in phase with the alternating forces applied to it by the moving air. When air is moving outward radially in the spaces between the diaphragm and the fixed heads of the tubes, there will be a decrease in pressure on the side where greater acceleration or velocity takes place thus providing the driving force nec essary to keep the diaphragm in vibration. When the diaphragm is near the jet, more air passes through the orifice in the diaphragm than when it is far away. This difference in air flow alsowill be increased by turbulence in the jet, caused, for example, by counterboring the jet orifice (see Figure 7) as at 20.

The action of the diaphragm is, therefore, to amplify the variations of the discharge rate of the jet and increase the variations of pressure generated in the jacket.

As described above, the diaphragm preferably has a high natural frequency and responds only to forced vibrations of frequency, controlled, primarily, by the resonator, modified to some extent, by the other coupled resonant components of the device, viz., the jet tube and the horn attached to the jacket. Any variation in coupling, frequency, or acoustic load, of any part of the device, will have some reaction on the frequency or pitch and quality of sound produced, but, due to the strong and sharp response of a resonator of this type, this component of the device will have the predominant effect in establishing the frequency of the system.

Since the jacket surrounding the jet is actually the region in which the acoustic power is generated previous to its transmission to the horn, any additional tubes or vents 2| attached to, or formed in, the jacket and having selective dissipation or response, will alter the quality of the tone produced.

The structural embodiment of the invention shown in the drawing utilizes a cylindrical casing ll] constituting the resonator. The only entrance into the resonator is through the small orifice I l. The end wall of the resonator, including the opening, is set in beyond the radial openings 2|. The diaphragm I8 is mounted over the end of the resonator so as to leave a space between the end wall of the resonator and the diaphragm, and the radial openings or vents 2| lead from this space to the atmosphere. The jet-tube I2 is in the form of a thimble including the orifice l3 aligned with the orifice [9 of the diaphragm and the orifice I l of the resonator. A nipple I4 is secured to the outer end of the thimble. The jacket or casing 16 surrounding the jet opening supports the jet-tube in position. This casing is of cylindrical form having one end fixed to the diaphragm close to its margin and the other end flanged inwardly and secured to the external surface of the jet-tube. A nipple extends radially from the jacket and the sound directing tube is attached to this nipple by any suitable means, such as a coupling 22.

Having described my invention, I claim:

1. A device of the class described, comprising, a resonator drum and a jet-tube, said resonator drum and jet-tube having opposing orifices in adjacent end walls thereof, said orifices closely spaced and co-axially disposed, said resonator drum closed with the exception of its orifice, and means for supporting said jet-tube and resonator in the described relationship.

2. A device of the class described, comprising, a resonator chamber closed with the exception of an orifice in one of its end walls, means for directing a jet of air through said orifice in a line toward the other end wall of the resonator chamber and a jacket surrounding the area of entry into the orifice to provide a region for generating acoustic power, said jacket including an outlet.

3. A device of the class described, comprising, a drum closed with the exception of a small opening in one end wall thereof and constituting a resonator, means for supplying a stream of air through said resonator opening toward the other end wall of the drum including a jet-tube, and means for jacketing and projecting the pulsations produced by the delivery of air from the jet into said resonator.

4. A device of the class described, comprising, a resonator consisting of a casing having a peripheral wall and end walls, said casing being closed with the exception of an opening in one of said end walls, and means for directing a stream of air co-axially into said opening.

5. A device of the class described, comprising, a resonator cylinder closed with the exception of a small opening in one end Wall, a jet-tube for delivering a stream of air into said resonator through said opening, a diaphragm interposed between the jet-tube and the opening of the resonator, said diaphragm having an opening aligned with the opening of the resonator, said diaphragm spaced from the end Wall of the resonator, a jacket surrounding the area of the opening into the resonator cylinder including an outlet for directing the acoustic power generated in the jacket, said resonator end wall and diaphragm including a space therebetween communicating with the atmosphere.

6. A device of the class described, comprising, a resonator cylinder closed with the exception of an orifice in its end wall, an air supply tube having an orifice in its end and arranged coaxially of the resonator orifice for directing a jet of air through the orifice of said resonator co-axially of the orifice and a jacket enclosing the space between the respective orifices to provide a region for generating acoustic power, said jacket including an outlet.

7. A device ofthe class described, comprising, a casing having a small opening in one end wall, a jet-tube for delivering a stream of air into said resonator through said opening, a wall interposed between the jet-tube and the opening of the resonator, said wall having an opening aligned with and larger than the opening of the resonator, said wall spaced from the end wall of the resonator, and a jacket enclosing the area between the jet-tube and the resonator and including an outlet for directing the acoustic power generated in the jacket.

8. A device of the class described, comprising, a chamber closed with the exception of a small opening in one end thereof and constituting a resonator, means for supplying a jet of air axially through said resonator opening, and means for jacketing and. projecting the pulsations produced by the delivery of the jet of air into said resonator.

9. A device of the class described, comprising, a resonator closed with the exception of an opening in one end wall thereof, means for delivering a stream of air into said resonator, a diaphragm interposed between said means and the opening of the resonator, said diaphragm having an ofpening aligned with the opening of the resonator, said diaphragm spaced from the-wall of the resonator opposite to the Wall having the opening, a jacket surrounding the jet including an outlet for directing the acoustic power generated in the jacket, said resonator end wall and said diaphragm including a space therebetween communicating with the atmosphere, and a sound projecting tube connected to said outlet.

10. A device of the class described, comprising, a resonator chamber and a jet-tube, said resonator chamber and jet-tube having opposing orifices closely spaced and co-axially disposed, the orifice of said jet-tube having its bore grooved, said chamber closed with the exception of its orifice and means for supporting said jettube and resonator chamber in the described relationship.

11. A device of the class described, comprising, a resonator cylinder closed with the exception of an opening in one wall thereof, means for supplying a stream of air into the opening of said resonator cylinder, and means for jacketing the entrance to the resonator and projecting the pulsations produced by the delivery of the stream of air into said resonator cylinder.

WALTER A. GARRA'I'I. 

